Rates of reaction in a sodium thiosulphate and hydrochloric acid solution.

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James Gillett SC1 Chemistry

Aim: -

To investigate the effects of changes in concentration of sodium thiosulphate on the rate of its reaction with hydrochloric acid. The word equation of the reaction is: -

Sodium Thiosulphate        + Hydrochloric Acid         Sodium Chloride        + Water        + Sulphur Dioxide        + Sulphur

     Na2S2O3 (aq)        + 2HCl (aq)         2NaCl (aq)        + H2O (l)        + SO2 (g)        + S (s)

Introduction: -

I am going to be testing the effect that the concentration of sodium thiosulphate solution has on the rate of reaction when mixed with hydrochloric acid.

When these two chemicals start out they are both clear liquids.  As they react after being mixed together the solution gets cloudy.  In order to measure the time taken to react I shall use a simple method.  I shall draw a cross on a piece of white paper and put it under the conical flask containing the solution.  When can no longer see the cross, I shall stop the stopwatch.  

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I predict that the greater the concentration of thiosulphate solution the faster the reaction, and so the faster the solution will go cloudy. I will use different concentrations so that I will get a good range of results.  

If when I have got my results it turns out to be true that the times taken by the reactions do decrease I shall actually plot "1 over Time taken", i.e. the "reciprocal" of the time taken.  This is because plotting the reciprocal will produce a graph showing a positive correlation.

Apparatus: -

I decided to use these concentrations ...

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